An automobile engine typically includes a timing chain for transmitting power from a crankshaft sprocket to one or more camshaft sprockets. A typical conventional timing chain is a roller chain having inner and outer link plates 510 and 550 respectively, of the type illustrated in FIG. 8. The peripheral edges of these plates that come into sliding contact with a chain guide have concave, arc-shaped surfaces 511 or 551 for retaining lubricating oil in order to reduce friction generated as the chain slides on an between an arc-shaped chain guide G1 or a linear chain guide G2. Such a chain is described in greater detail in United States Patent Publication 2006-0079363, published Apr. 13, 2006, the disclosure of which is incorporated by reference.
In the conventional roller chain link plate, the distance from one end of each arc-shaped surface 511 or 551 to the other end is equal to or greater than the chain pitch P, which is the distance between the centers of successive connecting pins in the chain, which are press-fit into pin holes in the outer link plates of the chain.
As shown in FIG. 8, tensile stress is concentrated, and fatigue fracture is liable to occur, in plate regions E, which are located along imaginary lines in the plate which extend, through the centers of bushing holes 512 in an inner link plate 510 or through the centers of pin holes 552 in an outer link plate 550, in directions perpendicular to the direction of elongation of the chain. Since the ends of the arc-shaped surfaces are located either within or beyond the region E, the end of region E has a cut out shape at location F, as seen in the enlarged auxiliary view in FIG. 8. Stress due to sliding contact with an arc-shaped chain guide G1, or a linear chain guide G2, acting on this plate region E, can cause chain breakage. Thus, there is a need for a way to improve the strength of the plate region E.
Furthermore, as shown in FIG. 8, the contact regions Z, over which link plates come into contact with the linear chain guide G2, are very small. Because the contact regions are small, retention of lubricating oil can be insufficient, and resistance to sliding is generated in these contact regions, resulting in impaired durability of the inner and outer link plates.
The invention addresses the above-described problems by providing a transmission chain for use in an engine, in which the link plate strength is improved in the regions where tensile force is concentrated and fatigue failure is liable to occur, and in which lubricating oil is more reliably retained between the link plates and the chain guides on which the chain slides, so that improved durability of the chain is achieved.